Ceiling mounted overhead patient lift systems typically operate like a winch and usually include a housing or frame affixed to a rail in the ceiling, a lift motor installed within the housing, a cylindrical lift drum inside the housing and driven by the lift motor, and a lift strap affixed at one end within the lift drum for lifting or lowering a patient when the drum is rotated and the strap is respectfully either wound up on the lift drum or paid out from the lift drum. A portable patient lift typically operates like a pneumatic hoist having a lift arm connected to one or more pneumatic (or hydraulic) cylinders for lifting or lowering a patient. Such lifts are known for use in connection with the lifting of patients for any number of reasons. One such reason is for weighing patients that are not capable of standing by themselves on a scale, as with patients confined to wheelchairs, or bariatric patients who have had weight loss surgery.
There are several known ways of weighing a patient using an overhead lift, one of which is to install a portable in-line tension scale between the sling bar and either (1) the lift strap of a motorized ceiling lift or portable patient lift, or (2) the lifting end of the lift arm of a portable patient lift. One such in-line scale is the LikoScale 350 sold by Liko AB. The in-line scale is connected at its top end to either the free hanging end of the lift strap in a ceiling mounted lift or portable lift, or the lift end of the rigid lift arm of a portable patient lift. Then the sling bar is connected to the lower end of the in-line scale. When a load is lifted by either lift, the in-line scale is placed in tension, and thus measures the patient's weight.
However, there are several drawbacks to such an in-line scale. First, utilizing an in-line scale reduces the lift height available to fully lift a patient off the ground or out of a chair or bed by as much as 8 inches, due to the length of the in-line scale. Depending on the height of the ceiling in a patient room, which in many hospitals may be fairly low, this reduced lift height may prevent a patient seated in a patient sling below the sling bar from being fully lifted off a bed, chair, or other support and otherwise make it difficult to accurately measure the patient's weight.
Second, in-line scales are powered by traditional batteries, which eventually become discharged and need to be replaced. When the scales lose power, the batteries must be replaced, but an operator may not have replacement batteries on hand or even nearby. Utilizing rechargeable batteries in the scale would still require that either they periodically be removed for recharging in a separate charger, or that the entire scale be removed from the lift and plugged into a wall outlet for recharging. In addition, periodically plugging the entire scale into a wall outlet will typically mean the scale would need to be removed from the patient lift, which can be time consuming each time the scale is installed and removed from the patient lift.
Accordingly, there is a need for a device with which to measure the weight of a patient using a patient lift, without reducing the available lift height of the patient lift, or at least minimizing the reduction in the available lift height of the patient lift. Further, there is a need for a device with which to measure a patient's weight using a patient lift, while eliminating any electrical connection between an external power supply and either of (1) the direct electrical inputs for powering the patient scale, or (2) the terminals of rechargeable batteries that may provide power to the patient scale. Still further, there is a need for a battery powered patient weighing device whose batteries can periodically be recharged before they lose power and without having to either remove them from the device or remove the device from the patient lift.
One solution to the aforementioned issues, as will be disclosed herein below, is to utilize a sling bar with an integrated scale, eliminating the need for a separate in-line scale to be connected thereto. However, one additional issue may arise with this proposed solution, in that if the active load suspended from the sling bar is not properly balanced or centered below the sling bar, the unbalanced weight may cause the sling bar, and accordingly the load cell of the scale integrated therein, to tilt at an angle from its normal balanced position. This means that a load axis of the load cell would become tilted or angled at some angle to the vertical direction of gravitational force, resulting in errors in the accuracy of any measurements taken by the load cell while in that position. This would ultimately result in inaccurate weight measurements. Accordingly, there is also a need for a way to compensate for any tilting of the sling bar that occurs during active loading, which tilting might otherwise angle the load axis of the load cell out of alignment with the vertical direction of gravitational force and affect the accuracy of weight measurements taken by the load cell of the scale.